1. Field of the Invention
This invention relates to an applicator for a heating treatment, and particularly, to an applicator for a heating treatment, wherein a predetermined portion in a living body is locally heated for treatment by the electromagnetic waves.
2. Description of the Prior Art
In recent years, the heating treatment, which may be referred to as "Hyperthermia", has been highlighted. There have been successive research reports to the effect that, particularly, a malignant tumor is continuously heated at about 43.degree. C. for one or two hours for example, and this treatment is repeated in predetermined cycles, whereby the regenerating function of a cancerous tissue is hampered, so that the most part of the cancerous tissue can be killed (F. K. Storm: Hyperthermia In Cancer Therapy, C. K. Hall Med. Pub. Boston (1983)). The heating treatment of this type is divided into two parts including a generally heating treatment and a localized heat treatment. For the localized heating treatment, wherein only cancerous tissue and therearound are selectively heated, a method of heating by the electromagnetic waves, a method of heating by the electromagnetic induction, a method of heating by the ultrasonic waves, and the like, have been proposed.
On the other hand, the inventors of the present invention have heretofore been proposing the effectiveness, in the case of heating a cancer in the deep portion of the living body, of treatment by electromagnetic waves and have been researching along this line. In this case, for the applicator for delivering the electromagnetic waves into the living body, the inventors have adopted a method of providing therewith an electromagnetic lens necessary to focus the energy of the electromagnetic waves. More specifically, as shown in FIGS. 1 and 2, an applicator 1 includes an electromagnetic wave feed section 2, a case body waveguide section 3 and an electromagnetic lens section 4 provided in an electromagnetic horn. An output stage of this electromagnetic lens section 4 is provided with a solid cooling plate 5 for preventing the surface of the living body from being overheated, and the solid cooling plate 5 may be cooled by cooling water. As shown, in FIG. 2, in the electromagnetic lens section 4, there are provided metal plates 6A, 6A, . . . at regular intervals `a`. The sides of the metal plates 6A which receive the electromagnetic waves are formed generally concavely as shown in FIG. 3 for converting the spherical electromagnetic waves delivered from the feed section 2 into the planar electromagnetic waves. Further, to focus planar waves formed through the action of the concave portion, in the central portion of the discharging sides of the electromagnetic lens section 4, there are arranged shorter metal plates as shown in FIG. 4, whereby the metal plates are generally concavely arranged and fixed.
On the other hand, the conventional example presents the following disadvantages.
(1) In considering the transmission system for the applicator as a whole, not shown, including electromagnetic wave generating means such as a magnetron or the like, the interior of the applicator would become heated and output from the applicator disadvantageously decreased, if the electromagnetic waves in the applicator are not matched with the generated waves. This occurs because the reflected waves would increase to generate standing waves.
(2) In the waveguide portion of the feed section 2 and the waveguide portion of the electromagnetic section 4, the propagated energy is concentrated at the central portion of the respective waveguides as shown in FIG. 5(1), and the concentrated energy, as it is, is delivered to the electromagnetic lens section 4, so that an original lens effect cannot be satisfactorily displayed in the electromagnetic lens section 4. More specifically, if the electromagnetic waves shown in FIG. 5(1) (now, the electromagnetic waves are assumed to be microwaves of TE.sub.10 mode), as they are, are delivered into the electromagnetic lens section 4 for example, then the intensities of the excitation in the respective zones partitioned by the intervals `a` are 0.90, 0.62 and 0.22, respectively, when the field intensities are normalized in the center zone in consideration of dividing the interior of the waveguide 3 into seven parts, whereby a distribution as shown in FIG. 5(2) is obtained. Because of this, the distribution of energy on the side of the inner wall of the waveguide is small, whereby satisfactorily focused electromagnetic waves cannot be formed in the electromagnetic lens section 4, thus presenting a disadvantage such that heating of the deep portion in the living body is hampered.
(3) In the waveguide portion, the inner dimension of the propagated electromagnetic waves in a direction of the magnetic field component must be set within a range between one half wavelength and one wavelength from the relationship of transmitting propagation. In consequence, when consideration is given to the case where the interior of the applicator forms a cavity, i.e. the interior is filled up with a gas such as air for example, one half wavelength substantially equals to 50 cm when a frequency used is 300 MH.sub.Z. Because of this, when a rapid treatment is required in particular, the applicator as a whole would need to be large in size, thus presenting the disadvantages that difficulties are encountered in handling the applicator, an appliance for fixing the applicator to the living body would also need to be large and rapid treatment is impracticable.
(4) Bubbles are stagnant in the applicator when it is used for a long period of time, whereby output of the electromagnetic waves from the applicator is disadvantageously decreased with time.
(5) In treating a cancer in the living body, there are many cases where the central portion of the cancer is shifted from a position at which applicator is fixed. In such cases, it takes much labor to detect the central position of the cancer and to fix the applicator onto the living body, thus presenting a disadvantage in that rapid treatment cannot be done.